A versicle is the first half of a preces, said or sung by an officiant or cantor, and answered with a said or sung response by the /People or choir.
For example, in the following opening of the Anglican service of Morning Prayer according to the Book of Common Prayer, the first line is the versicle and the second is the response (represented here by an O for Officiant and P for People of God).
In some liturgical books (such as hymnals or breviaries), the symbol "V" or "℣" is used.